JotYou is location based messaging for US cell phones. You can send a message to your friends so they get it when they arrive at a specific location. You send a message to one person or many people, and specify a delivery time and location using the Google map on the computer, or by specifying an address from your mobile. When they arrive at the location you specify, JotYou alerts them by buzzing their cell phone, and delivering the message.
JotYou also has a tracking feature that you can enable for fun games, events, and contests. The event organizer creates a tracking group, and can watch the locations of participants on the map as the event proceeds, and the times they were at those locations. The tracker only works when you allow it to, and visibility of location data is restricted by the group owner.
To use, install JotYou software on your mobile phone and log in to the mobile application using this same login information. JotYou now supports both GPS and WiFi Positioning. JotYou works with Windows Mobile 5 and 6, BlackBerry (Cingular/ATT, Sprint/Nextel), Nokia and other Java/J2ME smartphones.